Agricultural compositions comprising pH buffers, pH indicators, and pH sensitive agrochemicals

ABSTRACT

The invention provides a concentrate for dilution with water in the preparation of an agriculatural composition for application to crops, soil or animals and comprising an agricultural chemical whose agricultural activity varies with the pH of the water; and the invention provides a method of preparing such agricultural composition by mixing the concentrate with water and effecting such pH modification to the composition as is necessary to obtain a pH in the composition at which the agricultural activity of the chemical is acceptable. The concentrate comprises an active ingredient and a pH indicator for colouring the water, and the proportions of pH indicator and active ingredient are selected so that when the concentrate is diluted with water to provide an effective concentration of active ingredient in the water, the pH indicator indicates visually whether or not the pH of the water is suitable for acceptable agricultural activiy of the chemical.

This is a division of application Ser. No. 07/690,395, filed Apr. 25,1991, now U.S. Pat. No. 5,278,132, which is a continuation of Ser. No.07/012,027, filed Feb. 9, 1987, now abandoned.

This invention relates, broadly, to agricultural compositions. Moreparticular it relates to a concentrate for dilution with water in thepreparation of an agricultural composition for application to crops,soil or animals and comprising an agricultural chemical whoseagricultural activity varies with the pH of the water, and to a methodof formulating such agricultural composition.

In accordance with the invention there is provided a concentrate fordilution with water in the preparation of an agricultural compositionfor application to crops, soil or animals and comprising an agriculturalchemical whose agricultural activity varies with the pH of the water,the concentrate comprising an active ingredient and a pH indicator forcolouring the water, the proportions of active ingredient and pHindicator in the concentrate being selected so that when the concentrateis diluted with water to provide an effective concentration of activeingredient in the water, the pit indicator indicates visually whether ornot the pH of the water is suitable for acceptable agricultural activityof the agricultural chemical.

The invention accordingly applies to agricultural chemicals which havean agricultural activity which varies with the pH of water in the sensethat they are sensitive to degradation under alkaline or acidconditions, owing e.g. to hydrolysis thereof under alkaline conditions.When these compositions are used, for example in areas where the watersupply such as dam/river water has a pH unsuitable for the agriculturalchemical in question, e.g. hard waters which are too alkaline, thefarmer or other user typically modifies the pH of the water whereby theagricultural chemical is diluted, so that the water is in an acceptableand preferably optimum pH range to ensure optimum or at least acceptableagricultural activity of the chemical in question. This is effected byadding to the water a suitable adjuvant, e.g. an acid adjuvant when thewater is too alkaline. For most agricultural chemicals which are alkalisensitive or acid sensitive, there is a body of learning in connectionwith the optimum or at least acceptable pH range for good agriculturalactivity of the chemical in question. Typically the pH of the watersupply is measured, and a suitable quantity of adjuvant is added to thewater to obtain the desired pH. Field staff must accordingly be equippedto carry out the work involved, e.g. with pH meters, pH indicators (pHsensitive paper or chemicals) or the like, which pH meters can beexpensive, bulky and inconvenient, and pH strips can degrade and becomeunreliable with excessive temperatures. The present inventionaccordingly seeks to avoid pH determinations or measurements, and toprovide for automatic and immediate visual identification of the desiredor an acceptable pH during preparation of the agricultural composition.

Typically, the concentrate will contain water as a diluent to facilitatehandling and measurement of the concentrate and to dissolve or dispersethe various ingredients therein.

The concentrate may thus contain water, being a liquid, the activeingredient being an agricultural adjuvant for enhacing the activity ofan agricultural chemical in an aqueous chemical composition. Thisadjuvant will typically be a pH modifying agent selected from the groupcomprising acids, alkalis and buffers for controlling and modifying thepH of water.

For use in areas where the available water, such as ground/boreholewater or river water is alkaline, the adjuvant may be an acid selectedfrom the group comprising acetic acid, orthophosphoric acid and citricacid, and, although less preferred, hydrochloric acid, sulphuric acid,nitric acid or formic acid.

Naturally, if the available water is too acid, an alkaline pH modifyingagent will be employed, e.g. a member of the group comprising ammonia,potassium hydroxide and sodium hydroxide.

In certain cases the adjuvant may in fact be a buffer, being a member ofthe group comprising ammonia, mono ammonium phosphate, monopotassiumphosphate, phosphoric acid, sodium acetate and potassium hydrogenphthalate. In this case the concentrate may, in addition to the buffer,also comprise an agricultural chemical whose agricultural activityvaries with the pH of water with which it is in contact and whoseagricultural activity is acceptable in the pH range to which the bufferbuffers water to which it is added. Admixing of this concentrate withwater will automatically, within limits, show whether or not theeventual composition is within an acceptable pH range.

Instead, the concentrate may comprise, in addition to the buffer, anacid or alkali for modifying the pH of water, the buffer serving toguard against excessive pH modification arising from overdosing with theconcentrate.

Instead of being an adjuvant, the active ingredient in the concentratemay be an agriculatural chemical whose agricultural activity varies withthe pH of water with which it is in contact.

In this case, the concentrate may again contain water, being a liquid,the active ingredient being an agricultural chemical whose activityvaries with the pH of water with which it is in contact. In this case,in preparing the agricultural composition from the concentrate, theconcentrate will be added to the water, and a separate adjuvant willtypically be used, if necessary, in advance to modify the pH of thewater to the desired value. Field staff will know in advance, from priorexperimentation or usually from manufacturer's specifications and/orofficial regulations, what concentration of active ingredient isnecessary for the agricultural composition in question, i.e. itsappropriate dilution in water. The proportion of pH indicator in theconcentrate will accordingly be related to the proportion of activeingredient therein so that, when an appropriate mount of concentrate isadded to water in preparing the agricultural composition to provide theagricultural composition with the intended concentration of activeingredient, the composition will automatically contain a sufficientproportion of pH indicator for easy visual pH determination. The pHindicator in turn will be chosen so that it can indicate, e.g. byundergoing a colour change or by having a distinctive colour at asuitable pH, when the desired or an acceptable pH has been attained.Field staff accordingly my simply add the appropriate or prescribedamount of the concentrate to the water, and, thereafter, addprogressively increasing amounts of the appropriate adjuvant to thewater until the colour change takes place, or the appropriate colour isattained.

In this case, ie when the concentrate contains the agricultural chemicalwhose activity varies with the pH of water with which it is in contact,the active ingredient may be selected from the group comprisingpesticides, defoliants, desiccants and plant nutrients. Naturally, a pHcolour indicator will be selected which is compatible or inert asregards the other constituents of the concentrate, in particular theagricultural chemical in the concentrate.

The active ingredient may be a pesticide, selected from the groupcomprising insecticides, nematocides, fungicides and herbicides; andpossibly molluscicides and rodenticides. More particularly, the activeingredient may be selected from the group comprising organophsophates,carbamates, benzimidazoles dicarboxamides, bipyridols, pyrethroids andchlorinated hydrocarbons. Typical examples are azinphos methyl, benomyl,captan, dimethoate, ethyl parathion, methomyl, trichlorfon, oxamyl,dibrom, dimecron, mevinphos, monocrotophos, paraquat diquat,cypermethrin and dicofol. Of these, azinphos methyl, dimethoate, ethylparathion, trichlorfon, dibrom, dimecron, mevinphos and monocrotophosare organophosphates; methomyl and oxamyl are carbamates; benomyl is abenzimidazole; captan is a dicarboxamide; paraquat and diquat arebipyridols; cypermethrin is a pyrethroid; and dicofol is a chlorinatedhydrocarbon.

It should be noted that many agricultural chemicals have optimumagricultural activity in a slightly acidic pH range of e.g. pH 4-6.

The pH indicator may be selected from the group comprising methyl red,resorcin blue, 2,5-dinitrophenol and chlorophenol red. The Applicant hasfound that a pH indicator which can be employed for a large range ofagricultural chemicals is methyl red in free base form, such as thatavailable from the Applicant under the trademark Colorite Oneformulation is a 0.1% m/m solution of methyl red in free base form, inan isopropyl alcohol solvent. This pH indicator changes from colourlessat a neutral pH of 7 (sometimes through a yellow stage) to pink in a pHrange of about 5.5-about 4.5, and to bright red at a pH of about 4.5 andlower.

Resorcin blue changes from red at pH 4.4 to blue at pH 6.4;2,5-dinitrophenol changes from colourless at pH 4 to yellow at pH 5.4;and chlorophenol red changes from yellow at pH 4.8 to red at pH 6.4.

The invention extends to a method of preparing an aqueous agriculturalcomposition for application to crops, soil or animals, and whichcontains an agricultural chemical whose agricultural activity varieswith the pH of water with which it is in contact, the method comprisingadmixing, with the water, a concentrate as described above and theagricultural composition, and effecting such pH modification to thecomposition as is necessary to obtain a pH in the composition at whichsaid agricultural activity is acceptable.

Any pH modification should preferably take place before the agriculturalchemical is added to the mixture. This prevents degradation of thechemical prior to modification of the pH, and avoids any colour maskingof the pH indicator hi the mixture by the agriculatural chemical.

The concentrate may comprise an adjuvant which is a pH modifying agent,so that adding the concentrate to the mixture acts to modify the pH ofthe composition, the agricultural chemical being added separately to themixture, and subsequently to the addition of the concentrate.

Instead, the concentrate may comprise the agricultural chemical, so thatadding the concentrate to the mixture acts to provide an agriculturallyeffective concentration of said chemical in the composition, any pHmodification being effected prior to addition of the agriculturalchemical, by adding a separate pH modifying agent to the mixture.Naturally, if it turns out that the water supply is initially at asuitable pH, no pH modification will be required.

In the case described above where the concentrate contains both a bufferadjuvant and an agricultural chemical whose agricultural activity varieswith the pH of water with which it is in contact, and whose agriculturalactivity is acceptable in the pH range to which the buffer buffers waterto which it is added, the concentrate may merely be admixed into theappropriate amount of water to prepare the intended agriculturalcomposition. When the concentrate has been added to water in proportionssufficient to provide it with the intended agricultural activity,sufficient buffer will simultaneously and automatically be added tobuffer the water to the appropriate pH range, and sufficient pHindicator will automatically be added to confirm that the water is inthis pH range. The proportions of pH indicator and buffer will thus beset in the concentrate bearing these requirements in mind and bearing inmind the nature of the agricultural chemical in the concentrate. In thiscase, it is contemplated that, only with available waters of extremelyhigh or extremely low pH ranges, will the buffer be unable to buffer thewater to the appropriate pH range for good agricultural activity of theagricultural chemical, and in these exceptional cases the pH indicatorwill indicate that suitable buffering has failed to take place.

For a large number of agricultural chemicals which are subject todegradation at unsuitable pH's, an acceptable or desirable pH range isthe pH range of 4-6. Methyl red has two colour changes within this rangeand is accordingly suitable for a large number of agriculturalchemicals, a pink colour indicating a suitable pH in the eventualagricultural composition.

It will be appreciated that the present invention is applicable to largenumbers of agricultural chemicals and that the concentrations of thesechemicals can vary substantially in the eventual formulated agriculturalcomposition for application to crops, soil or animals, depending, interalia, on the nature of the agricultural chemical itself, the purpose forwhich it is being used, climatic conditions, the half-life of theagricultural chemical in water of a particular pH, frequency ofapplication, the type of crop, environmental factors and economics, orthe like. In each case, the proportion of pH indicator included in theconcentrate will be related to the proportion of agricultural chemicaltherein, merely according to the criterion that sufficient pH indicatorshould be present when the concentrate has been added to water in theappropriate or intended dilution for the agricultural chemical, so thatthe pH indicator will be effective and visible at its dilution in thewater. In other words, when small amounts of concentrate will be addedto water, the proportion of pH indicator in the concentrate will behigh, and when large amounts of concentrate are added to water, theproportion of pH indicator therein can be correspondingly lower. For themanufacturer of the concentrate, who will be aware of its intended useand who will prescribe the concentrations at which it will be used, itwill be a simple matter to ensure that the concentrate containssufficient pH indicator to be effective when the concentrate is used atthese prescribed concentrations. Considerable and indeed radicalvariations in the proportions between the agricultural chemical and pHindicator in the concentrate are thus contemplated by the invention, andindeed the absolute concentrations of the agricultural chemical and pHindicator in the concentrate can also vary radically. The Applicant hasfound, however, that no difficulty is presented in determining suchabsolute concentrations and relative concentrations, by means of routineexperimentation. The proportion of pH indicator in the concentrate maythus vary considerably from one concentrate to another, depending on howmuch of the concentrate is intended to be added to water. Similarconsiderations apply when the concentrate contains an adjuvant ratherthan an agricultural chemical.

Naturally, the agricultural composition, whether it contains an adjuvantand/or an agricultural chemical, may also contain constituents such asspreaders, wetters or the like, such as those typically employed whenthe eventual agricultural composition is intended for foliarapplication, or spraying or dipping animals.

The invention will now be described, by way of non-limitingillustration, with reference to the following non-limiting Examples:

Acid adjuvants suitable for pH reduction, control and/or buffering inaqueous agricultural compositions for application to plants or soil andcontaining alkali-sensitive agricultural chemicals subject todegradation in alkaline environments were formulated to have thefollowing compositions:

EXAMPLE 1

    ______________________________________    Constituent            Parts by mass    ______________________________________    Nonyl phenoxy polyoxy- 10.4    ethylene glycol having    9-10 mole % of ethylene oxide    (Wetting Agent)    A mixture of the monoortho-                           43.6    phosphoric esters and    diorthophosphoric esters of    said nonylphenoxy polyoxyethylene-    glycol (Buffer)    Orthophosphoric acid (Acid Adjuvant)                           2.9    Isopropyl alcohol (Solvent and                           15.6    wetting agent)    Water                  25.6    Oleic acid (Acid Adjuvant)                           1.8    Colorite (pH Indicator)                           0.1    ______________________________________

EXAMPLE 2

    ______________________________________    Constituent            Parts by mass    ______________________________________    Acetic acid (Acid Adjuvant)                           77.1    Ammonia (as acetate or amide) (Buffer)                           7.3    Water                  15.5    Colorite (pH Indicator)                           0.1    ______________________________________

In Example 2 the acetate or amide ammonium salt added was added in aproportion equivalent to 7.3 parts by mass ammonia.

It was found that, when these adjuvants were used to control or maintainthe pH of various aqueous mixtures for application to plants or soil andcontaining alkali-sensitive agricultural compositions (insecticides,fungicides, herbicides, defoliants or the like) subject to degradation,use of the adjuvants in the usual quantities for pH control, adjustmentor maintenance in the mixtures provided mixtures whose pH could easilybe visually determined by their colour, ie colourless or yellowish atpH's above 5.5, pink in the pH range 5.5 to 4.5 and bright red at pH'sbelow 4.5.

It is an advantage of the invention that it provides a rapid andaccurate method of making and/or maintaining an aqueous agriculturalchemical composition at its optimum pH range and promotes stability ofthe chemical and optimal agricultural efficacy with alkaline waters.Moreover, field staff are saved the necessity of calculating the preciseamount of adjuvant to be added to the composition, and need not beskilled.

It is a further advantage of the invention when the colouring agent isemployed in an agricultural composition other than an adjuvant, ie onewhose active ingredient is subject to degradation, that it will indicateif the water supply is in fact within a desired or optimum pH range anddoes not require pH adjustment.

We claim:
 1. A concentrate comprising a mixture of a pH indicator forcoloring water, an agricultural chemical for application to crops, soilor animals, and a pH modifying agent for modifying pH of water withwhich the concentrate is diluted, the agricultural chemical having anactivity that varies with the pH of the water and having an acceptableagricultural activity at a pH within the range of 4-6, wherein theproportions of pH modifying agent, pH indicator and agriculturalchemical in the concentrate are such that, when the concentrate isdiluted with water to provide an effective concentration of theagricultural chemical and the pH of the water is modified by the pHmodifying agent, the pH indicator indicates visually when the pH of thewater is in the range of 4-6.
 2. A concentrate as claimed in claim 1, inwhich the agricultural chemical is a compound selected from the groupconsisting of pesticides, defoliants, desiccants and plant nutrients. 3.A concentrate as claimed in claim 2, in which the agricultural chemicalis a pesticide selected from the group consisting of insecticides,nematocides, fungicides and herbicides.
 4. A concentrate as claimed inclaim 3, in which the agricultural chemical is a compound selected fromthe group consisting of organophosphates, carbamates, benzimidazoles,dicarboximides, bipyridols, pyrethroids and chlorinated hydrocarbons. 5.A concentrate as claimed in claim 4, in which the agricultural chemicalis a compound selected from the group consisting of azinphos methyl,benomyl, captan, dimethoate, ethyl parathion, methomyl, trichlorfon,oxamyl, dibrom, dimecron, mevinphos, monocrotophos, paraquat, diquat,cypermethrin and dicofol.
 6. A concentrate as claimed in claim 1, inwhich the pH modifying agent comprises an agricultural adjuvant forenhancing the activity of the agricultural chemical in an aqueousagricultural composition.
 7. A concentrate as claimed in claim 6, inwhich the pH modifying agent is selected from the group consisting ofacids, alkalis and buffers for controlling or modifying the pH of water.8. A concentrate as claimed in claim 7, in which the pH modifying agentcomprises an acid selected from the group consisting of acetic acid,orthophosphoric acid and citric acid.
 9. A concentrate as claimed inclaim 7, in which the pH modifying agent comprises a buffer selectedfrom the group consisting of ammonia, monoammonium phosphate,monopotassium phosphate, phosphoric acid, sodium acetate and potassiumhydrogen phthalate.
 10. A concentrate as claimed in claim 1, in whichthe pH indicator comprises a member selected from the group consistingof methyl red, resorcin blue, 2,5-dinitrophenol and chlorophenol red.11. A concentrate as claimed in claim 10, in which the pH indicatorcomprises methyl red in free base form.
 12. A concentrate as claimed inclaim 4, in which the pH modifying agent comprises an acid selected fromthe group consisting of acetic acid, orthophosphoric acid and citricacid.
 13. A concentrate as claimed in claim 12, in which the pHmodifying agent comprises a buffer selected from the group consisting ofammonia, monoammonium phosphate, monopotassium phosphate, phosphoricacid, sodium acetate and potassium hydrogen phthalate.
 14. A concentrateas claimed in claim 12, in which the pH indicator comprises a memberselected from the group consisting of methyl red, resorcin blue,2,5-dinitrophenol and chlorophenol red.
 15. A concentrate as claimed inclaim 13, in which the pH indicator comprises a member selected from thegroup consisting of methyl red, resorcin blue, 2,5-dinitrophenol andchlorophenol red.
 16. A concentrate as claimed in claim 14, in which theagricultural chemical is a compound selected from the group consistingof azinphos methyl, benomyl, captan, dimethoate, ethyl parathion,methomyl, trichlorfon, oxamyl, dibrom, dimecron, mevinphos,monocrotophos, paraquat, diquat, cypermethrin and dicofol.
 17. Aconcentrate as claimed in claim 15, in which the agricultural chemicalis a compound selected from the group consisting of azinphos methyl,benomyl, captan, dimethoate, ethyl parathion, methomyl, trichlorfon,oxamyl, dibrom, dimecron, mevinphos, monocrotophos, paraquat, diquat,cypermethrin and dicofol.
 18. The concentrate of claim 1, wherein saidagricultural chemical is subject to degradation outside of said pH rangeof 4-6.
 19. A process for preparing an agricultural composition which issuitable for application to crops, soil or animals, comprising:(a)providing a concentrate comprising a mixture of a pH indicator forcoloring water, an agricultural chemical for application to crops, soilor animals, and a pH modifying agent for modifying pH of water withwhich the concentrate is diluted, the agricultural chemical having anactivity that varies with the pH of the water and having an acceptableagricultural activity at a pH within the range of 4-6, wherein theproportions of pH modifying agent, pH indicator and agriculturalchemical in the concentrate are such that, when the concentrate isdiluted with water to provide an effective concentration of theagricultural chemical and the pH of the water is modified by the pHmodifying agent, the pH indicator indicates visually when the pH of thewater is in the range of 4-6; and (b) diluting said concentrate withwater so as to effect a color change of the pH indicator of saidconcentrate.
 20. The process of claim 19, wherein in said providingstep, said agricultural chemical is a compound selected from the groupconsisting of azinphos methyl, benomyl, captan, dimethoate, ethylparathion, methomyl, trichlorfon, oxamyl, dibrom, dimecron, mevinphos,monocrotophos, paraquat, diquat, cypermethrin and dicofol; said pHmodifying agent includes an acid selected from the group consisting ofacetic acid, orthophosphoric acid and citric acid, and further includesa buffer selected from the group consisting of ammonia, monoammoniumphosphate, monopotassium phosphate, phosphoric acid, sodium acetate andpotassium hydrogen phthalate; and said pH indicator includes a memberselected from the group consisting of methyl red, resorcin blue,2,5-dinitrophenol and chlorophenol red.